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Method of filling through-holes

a technology of through-holes and copper plating, which is applied in the direction of liquid/solution decomposition chemical coatings, coatings, printed circuit manufacturing, etc., can solve the problems of copper plating's tendency to fill through-holes, the difficulty of copper plating's high aspect ratio, and the way it tends to fill, so as to reduce or inhibit the formation of dimples and voids, good through-hole filling, and the effect of improving throwing power

Inactive Publication Date: 2014-09-18
ROHM & HAAS ELECTRONICS MATERIALS LLC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The invention reduces or prevents the formation of dimples and voids during the filling of through-holes. Dimples are tiny and can be less than 10 μm deep. This reduced depth of the dimples and void area improves the flow of copper during the process, resulting in a more uniform layer of copper on the surface of the substrate and better filling of the through-holes.

Problems solved by technology

Filling the through-holes by copper plating has become more and more difficult with higher aspect ratios.
This results in larger voids and deeper dimples.
Another problem with through-hole filling is the way they tend to fill.
If the right combination of additives is not chosen then the copper plating results in undesired conformal copper deposition.
Often the copper fails to completely fill the through-hole and both ends remain unfilled.
Entire dimple elimination during through-hole filling is rare and unpredictable.
Larger dimples affect further processing of the panel and larger voids affect device performance.
Another problem associated with through-hole filling is filling through-holes with electrolytic copper when the through-hole walls have a layer of flash copper.
Such electroless copper layers tend to oxidize.
Prolonged periods of exposure to air as well as general handling of the boards result in relatively rapid oxidation of the electroless copper layer.
Also, the thicker flash copper layer allows for removal of any oxide formation during storage by conventional etching processes whereas such etching cannot be done on the thinner electroless copper without the danger of damaging or removing the electroless copper layer.
Unfortunately, electrolytic copper flash adds to the difficulty of filling through-holes.
Dimpling and void formation frequently occur when workers try to fill through-holes using electrolytic acid copper plating baths.

Method used

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Examples

Experimental program
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Effect test

example 1

[0033]63 mmol of 1,4-Butanediol diglycidyl ether (monomer 1), 25 mmol of imidazole (monomer 2) and 75 mmol of 4-phenylimidazole (monomer 3) were added at room temperature into a round-bottom reaction flask. Then, 30 ml of DI water was added to the flask. The initially formed white colored suspension eventually disappeared as the reaction temperature increased and turned into a phase separated mixture. The reaction mixture was heated for 2 hours using an oil bath set to 98° C. After adding 2 ml of concentrated sulfuric acid into the reaction flask, the solution became transparent with a light-yellow color. The mixture was heated for an additional 3 hours and left stirring at room temperature for another 8 hours. The resulting amber colored reaction product was transferred into a volumetric flask, rinsed and diluted with 0.5-1% sulfuric acid. The reaction product solution was used without further purification. Analysis of the reaction product by 1H NMR (500 MHz, DMSO-d6) showed the fo...

examples 2

[0035]Two FR4 / glass-epoxy coupons 5 cm wide, 15 cm long and 100 μm thick with a plurality of through-holes were provided by Tech Circuit. The through-holes had an average diameter of 100 μm. The coupons were plated with electroless copper on the surface and in the through-holes. The thickness of the electroless copper layer was 0.3 μm.

[0036]One coupon was placed in a dessicator until further processing to discourage oxidation of the copper and the other was plated with a layer of flash copper by placing the electroless copper coupon in a plating cell which contained an acid copper electroplating bath with a formula as shown in Table 1.

TABLE 1COMPONENTAMOUNTCopper sulfate pentahydrate220g / LSulfuric acid40g / LChloride ion from hydrochloric acid50ppmPolyethylene glycol2g / L4-phenylimidazole / imidazole / 1,4-butandiol50mg / Ldiglycidyl ether copolymerBis-(sodiumsulfopropyl)-disulfide10mg / LWaterTo oneliter

[0037]The coupon was connected to a conventional DC rectifier. The counter electrode was a...

example 3

[0039]Two FR4 / glass-epoxy coupons 5 cm wide, 15 cm long and 100 μm thick with a plurality of through-holes were provided by Tech Circuit. The through-holes had an average diameter of 100 μm. Each coupon included a layer of electroless copper 0.3 μm. One coupon was placed in a dessicator and the other was electroplated with a flash copper layer 5 μm thick as described in Example 2 above. The coupon was then placed in the dessicator with the other coupon until further processing to discourage oxide formation on the copper.

[0040]Upon removing the coupons from the dessicator, both were cleaned using a conventional copper surface cleaner to remove any oxide and provide a clean copper surface for further processing. Each coupon was then placed into two separate plating cells containing the copper electroplating bath of Table 1. The counter electrodes were insoluble anodes. Acid copper electroplating was done at a current density of 1.5 A / dm2 with continuous air agitation of the baths for ...

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Abstract

The methods inhibit or reduce dimpling and voids during copper electroplating of through-holes with flash copper layers in substrates such as printed circuit boards. An acid solution containing reaction products of aromatic heterocyclic nitrogen compounds and epoxy-containing compounds is applied to the through-holes of the substrate followed by filling the through-holes with copper using a copper electroplating bath which includes additives such as brighteners and levelers.

Description

FIELD OF THE INVENTION[0001]The present invention is directed to a method of filling through-holes having a layer of flash copper which reduces or inhibits the formation of dimples and voids. More specifically, the present invention is directed to a method of filling through-holes having a layer of flash copper which reduces or inhibits the formation of dimples and voids by applying an aqueous acid pretreatment solution containing reaction products of aromatic heterocyclic nitrogen compounds with epoxy compounds at low concentrations to the through-holes with the flash copper layer followed by filling the through-holes with copper using an acid copper electroplating bath containing brighteners and levelers.BACKGROUND OF THE INVENTION[0002]High density interconnects is an important design in the fabrication of printed circuit boards with microvias and through-holes. Miniaturization of these devices relies on a combination of thinner core materials, reduced line widths and smaller dia...

Claims

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Application Information

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IPC IPC(8): C25D5/02C25D3/38
CPCC25D3/38C25D5/022C25D5/02C23C18/1653H05K3/423C25D5/34
Inventor JAYARAJU, NAGARAJANNAJJAR, ELIE H.BARSTAD, LEON R.
Owner ROHM & HAAS ELECTRONICS MATERIALS LLC
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